It occurs mainly as insoluble carbonates, sulphates and silicates, in crystal rocks. It is the sixth most abundant element following calcium. Magnesium occurs as dolomites (MgCO3.CaCO3), magnesites (MgCO3), epsomite (MgSO4.7H2O). It is further represented by common basaltic mineral olivine [(MgFe)2SiO4] and by soapstone (talc) Mg3Si4O10(OH2) , etc., as silicates.
It is fifth most abundant element in Earth's crust. It is found existing as whole mountain ranges of limestone, marble and chalk, in vast sedimentary rocks of CaCO3. Other important minerals containing calcium are gypsum (CaSO4.2H2O), anhydrite (CaSO4), fluorite (CaF2) and fluorapatite [3Ca3(PO4)2.CaF2].
It occurs as celestite (SrSO4) and strontianite (SrCO3).
The main ore of barium is baryte (BaSO4). It also occurs as witherite (BaCO3).
It is found as surface deposits of beryl in pegmatite rocks. Like Lithium it occurs in less abundance.
Radium occurs only in association with uranium, having a terrestrial abundance of approximately 10-6ppm.